10 research outputs found
Distributed physical sensors network for the protection of critical infrastractures against physical attacks
The SCOUT project is based on the use of multiple innovative and low impact technologies for the protection of space control ground stations and the satellite links against physical and cyber-attacks, and for intelligent reconfiguration of the ground station network (including the ground node of the satellite link) in the case that one or more nodes fail. The SCOUT sub-system devoted to physical attacks protection, SENSNET, is presented. It is designed as a network of sensor networks that combines DAB and DVB-T based passive radar, noise radar, Ku-band radar, infrared cameras, and RFID technologies. The problem of data link architecture is addressed and the proposed solution described
DVB-T-based passive radar for silent surveillance of drones
Nowadays, Unmanned Aerial Vehicles (UAVs) and drones are used as threat’s
vectors that create personal and public security issues. The unpredictable and
complex motion along with the small Radar Cross Section (RCS) and low velocity
makes the drone detection a challenging task for any radar system.
In the context outlined earlier, the security level enabled by conventional
active radar systems could be augmented by the cost-effective, non-intrusive and
eco-friendly Passive Radar (PR) technology. As a PR system does not have its own
transmitter, this allows reduced costs, intrinsic covert operation capability and the
lack of additional electromagnetic pollution. To guarantee complete and
continuous coverage, PR can effectively be integrated within conventional active
radars not only to extend the surveillance coverage, acting as ‘gap-filler’, but also
to reduce the probability of out of service of the surveillance system. Moreover,
aiming at the monitoring of airport terminal areas or harbours, where the installation
of additional sensors might be limited by regulations related to public safety
and risk of interference with pre-existing systems, a network of PRs could easily be
deployed to provide continuous and complete coverage.
The stationary nature and the isotropic characteristic of many of the employable
Illuminators of Opportunity (IoO) provide a persistent illumination of the
targets of interest to generate Coherent Processing Intervals (CPIs) of long integration
times (Tint) on receive to counteract the limited power density offered by
the emitter. This certainly applies to many ground-based transmitters for analogue
or digital radio/TV broadcasting. Among them, the emitters of the Digital Video
Broadcasting-Terrestrial (DVB-T) are particularly attractive for counter-drone
applications. Specifically, the high radiated power of these transmitters and the
excellent coverage make them suitable for the detection of these small RCS and
low altitude targets. In addition, the continuous emissions and the fine range
resolution of about 20 m (equivalent monostatic range resolution yielded by a
signal bandwidth of approximately 8 MHz) make them potentially able to continuously
detect and discriminate closely spaced targets. Aiming at the detection of
the low Signal-to-Noise Ratio (SNR) targets and at widening the DVB-T-based PR
coverage area, very long integration times (up to few seconds) can be exploited if
the migration effects are properly compensated. It is worth noticing that the use
of long integration time allows also to improve the Doppler resolution as well as to
discriminate between slowly moving targets and clutter contributions, which is of
particular interest in a scenario with a high density of targets. By employing an
Orthogonal Frequency-Division Multiplexing (OFDM) modulation, DVB-T signals
are noise-like waveforms; thus, they provide ambiguity function with attractive
properties that are nearly independent of the signal content and almost time-invariant. Eventually, since a DVB-T transmitter typically broadcasts multiple channels
at different carrier frequencies, this provides the desired diversity of information that
could be successfully exploited for both target detection and its localization.
Recently, different authors have investigated the use of such sensor for
counter-drone operations proving the capability of such technology to
detect and localize small and medium drones up to a few kilometres from the PR
receiver. Moreover, the capability of such sensor in simultaneous detection of
drones flying near the airport area along with the conventional civil air traffic at
farther ranges has been proved.
This chapter reports the latest results of DVB-T-based PR for counter-drone
operations obtained by the research groups of the University of Alcala´ and
Sapienza University of Rome
ON THE CODING GAIN OF DYNAMIC HUFFMAN CODING APPLIED TO A WAVELET-BASED PERCEPTUAL AUDIO CODER
This paper evaluates the coding gain of using a dynamic Huffman entropy coder in an audio coder that uses a wavelet-packet decomposition that is close to the subband decomposition made by the human ear. The subband audio signals are modeled as samples of a stationary random process with laplacian probability density function because experimental results indicate that the highest coding efficiency is obtained in that case. We have also studied how the entropy coding gain varies with the band index. The proposed adaptive Huffman coding method gives rise to an average coding gain of approximately 0.25 bits per sample compared to binary coding. A further coding gain can be achieved if timevarying filter banks are used. Experimental results tell us that using a suitable method to translate the psychoacoustic information to the wavelet domain, combined with our adaptive Huffman coding scheme, binary rates of about 64 kbps can be obtained for transparent coding of CD quality monophonic audio signals. 1
Distributed physical sensors network for the protection of critical infrastractures against physical attacks
The SCOUT project is based on the use of multiple innovative and low impact technologies for the protection of space control ground stations and the satellite links against physical and cyber-attacks, and for intelligent reconfiguration of the ground station network (including the ground node of the satellite link) in the case that one or more nodes fail. The SCOUT sub-system devoted to physical attacks protection, SENSNET, is presented. It is designed as a network of sensor networks that combines DAB and DVB-T based passive radar, noise radar, Ku-band radar, infrared cameras, and RFID technologies. The problem of data link architecture is addressed and the proposed solution described
Artificial Neural Network-Based Clutter Reduction Systems for Ship Size Estimation in Maritime Radars
The existence of clutter in maritime radars deteriorates the estimation of some physical parameters of the objects detected over the sea surface. For that reason, maritime radars should incorporate efficient clutter reduction techniques. Due to the intrinsic nonlinear dynamic of sea clutter, nonlinear signal processing is needed, what can be achieved by artificial neural networks (ANNs). In this paper, an estimation of the ship size using an ANN-based clutter reduction system followed by a fixed threshold is proposed. High clutter reduction rates are achieved using 1-dimensional (horizontal or vertical) integration modes, although inaccurate ship width estimations are achieved. These estimations are improved using a 2-dimensional (rhombus) integration mode. The proposed system is compared with a CA-CFAR system, denoting a great performance improvement and a great robustness against changes in sea clutter conditions and ship parameters, independently of the direction of movement of the ocean waves and ships